Energy saving has recently been desired because of the importance of preventing global warming, one of concerns over global environment. In every field, energy saving is promoted. Required for general equipment using heat or cold and members related to houses is a heat-insulating member having excellent heat-insulating performance in low- or medium-temperature areas ranging from −30 to 150° C., from the viewpoint of efficient use of heat. On the other hand, business equipment, such as a computer, printing machine, and copying machine, has a heating element in its inside. To prevent the heat from conducting from the heating element to toners or internal precision components susceptible to heat, a high-performance heat-insulating member capable of being used at temperatures around 150° C. is strongly desired.
Among general heat-insulating members used in a temperature range around 150° C., a vacuum heat insulator is used for applications requiring a heat-insulating member having higher performance. A vacuum heat insulator is structured so that a core holding a space made by minute voids is covered with an enveloping member for shielding entry of ambient air and the space is evacuated.
As the enveloping member of a vacuum heat insulator, a case of a heat-sealed metal can be used. In a low-temperature area requiring no heat resistance, a plastic-metal laminated film having a heat-seal layer, gas barrier layer, and protective layer, which is relatively easily bent and curbed, is often used as an enveloping member. Materials of the core include powders, fibers, and open-cell foams.
In recent years, there have been wider-ranging demands for vacuum heat insulators. Accordingly, vacuum heat insulators with much higher performance are required. To improve heat insulation by blocking the impact of radiation, a vacuum heat insulator using a calcium silicate mold including a radiant heat shield as a core is disclosed in Japanese Patent Unexamined Publication No. 10-160091. Also, to improve heat insulation, a vacuum heat insulator that uses granulated composition to which inorganic gel components and an infrared opaquer are added as a core is disclosed in Japanese Translation of PTC Publication No. 2001-502367. Disclosed in Japanese Patent Unexamined Publication No. 62-258293 is a technique in which a proper quantity of a synthetic resin film having a metal deposition surface formed thereon is mixed in powdered heat insulator so that the synthetic resin film intersects and opposes the direction in which heat permeates.
However, the infrared ray, i.e. a factor of radiant heat, is absorbed when it reaches the enveloping member on the surface of a vacuum heat insulator and, converted into heat energy to generate a state of solid heat conduction. For this reason, extremely little of the infrared ray reaches the core. Therefore, to improve heat insulation at temperatures around 150° C., suppression of transfer of radiant heat is necessary. The structures of these conventional techniques cannot address these problems sufficiently.